Engage: Remind students that a moving object has kinetic energy but an object at rest has potential energy. Say, "Today we are going to explore potential and kinetic energy when two objects collide." Begin with the following demonstration: Place 2 marbles about 6 inches apart on a table. Make sure one marble is motionless, then roll the other marble into it. Ask students, "What happened to the energy in the moving marble when it collided with the marble at rest?" (students may say it made the other marble move, etc.) Explain to the students that the energy from the moving marble was transferred into the object at rest and caused the marble to move. Ask, "But what would happen if both of these objects were moving and they collide?" Place the two marbles about 6 inches apart on the table directly in line with each other and at the same time push them into each other. (The marbles will most likely bounce off each other, change direction, and then roll to a stop.) Explain to the students that the energy in both of these moving objects was exchanged and during this collision, the exchange of energy also changed the motion of the marbles. Ask students if they observed any other forms of energy being transferred when the marbles collided (possible responses: sound energy when the marbles hit each other). Explain that when objects collide energy can be transferred into many different forms and later we will set up our own collisions to observe energy transfer.
Explore: Project the following website on the interactive whiteboard for whole class viewing: Gizmos Sled Wars.
Load the Gizmos Sled Wars. This Gizmo is an interactive energy game containing a Yeti named Burt who rides a sled down a steep hill. Click the presentation mode under the snow scene to set the simulation to full screen for better viewing. Point out to the students that the simulation uses 3 different variables: height, mass, and speed. By changing one or more of these variables, you are able to change the outcome of how many snowmen Burt destroys with his sled. Set the snowmen count to 5 by clicking inside the box next to the word snowmen and changing the default setting from 3 to 5. The height of the sled should automatically be set at 25.0 m which is the default setting. Check to make sure this is correct. If it needs to be changed, scroll over the sled until a hand appears then push the sled up the hill until the height reads 25.0 m. Click inside the Red Sled's mass and delete the default setting of 100 kg and type 50. You can also click the show energy box at the top and this will track the precise moment the sled's energy changes from potential to kinetic energy. Push the play button and tell the students to observe what happens. How many snowmen does Burt destroy? Notice a box will appear on the screen containing the sled's maximum speed, energy, and how many snowmen were destroyed. Make two classroom data charts (one for sled height 25.0 m and one for sled height 50.0 m) on the board to record data for this simulation (example in attachments). Include the mass, maximum sled speed, maximum sled energy, and the number of snowmen destroyed. These charts can also be copied and distributed to the students.
Click the reset button on the simulation, set the Red sled's mass at 100 kg, push play and record your data.
Click the reset button on the simulation, set the Red sled's mass at 150 kg, push play and record your data.
This time change the height of the Red sled by scrolling over the sled until a hand appears then push the sled up the hill and stop on 50.0 m, set the Red sled's mass at 50 kg, push play and record your data.
Repeat the simulation with a height of 50.0 m, and mass at 100 kg, and 150 kg, and record your data.
Ask students to compare the two data charts. What patterns do they see? (The data should clearly show when the height and mass increase so does the sled's speed, energy, and the number of snowmen it destroys. In order to destroy more snowmen, Burt has to increase his height, mass, and speed, which will increase his kinetic energy.) Place students in groups of four and distribute one piece of cardstock to each group. Ask students to create a friendly note to Burt advising him of what they think he will need to do in order to destroy all 5 snowmen. The note should address how Burt will need to change the sled height and mass in order to accomplish his goal (increase the height to 50.0 m and the mass to 200 kg or simply stating: If I increase the height and mass, then it will increase the speed and destroy all 5 snowmen). They may add appropriate illustrations and words of encouragement. Cards will be posted on the bulletin board for students to view.
Tell the students, "Now you are going to set up your own collisions to observe how energy transfers from one object to another first hand." Give each group 2 toy cars of equal size (this works best if all groups have toy cars of equal size and shape), 1 or 2 paper towel rolls to use as ramps, 20 metal washers or pennies, 3 or 4 textbooks, and tape. Print out the Collision Task Cards found under attachments and cut them apart. Give one card to each group. (If there are more than four groups, you will just have additional groups performing the same task.) Each group will build the ramp on their collision task card, then test and measure the distance caused by their collision. Next, they will create a presentation on Educreations website (https://www.educreations.com/) to share their findings with the class. Their presentation must include a photo, drawing, or video of their collision (rubric under attachments).